1. Field of the Invention
This invention relates to a wavelength conversion device in which an excitation light pulse is made incident on a nonlinear optical medium as incident light, SC (supercontinuum) light is generated in the nonlinear optical medium, and by filtering this SC light using an optical band-pass filter, conversion into an optical pulse of wavelength different from that of the incident light is performed.
2. Description of Related Art
Various means are being studied in order to construct large-capacity optical communication networks with transmission rates of 1 Tbit/s and higher. Among these, the technology attracting the most attention is wavelength division multiplexing (WDM). In order to realize a WDM optical communication network, a wavelength conversion device is deemed necessary. For example, if a wavelength conversion device is adopted in an optical cross-connect node (OXCN), it becomes possible to avoid collision between channels and to reutilize wavelengths; in addition, improvements in network management and in the network itself (upgrades) are facilitated. As a result, there is the advantage that new communication bands can be utilized.
Due to such demands, the wavelength conversion devices described below were developed. In such wavelength conversion devices, the natural law utilized to effect wavelength conversion is, for example, four-wave mixing (FWM) occurring in a nonlinear optical medium, such as in a semiconductor optical amplifier or similar (see for example Japanese Patent Application Laid-open No. 2000-66253).
Further, there has also been an attempt to realize a WDM optical communication network using a multiple-wavelength light source, by selecting the light generated by the multiple-wavelength light source and by allocation to different channels (see for example Japanese Patent Application Laid-open No. 2001-251253).
However, a wavelength conversion device utilizing FWM occurring in the gain region of a semiconductor optical amplifier, taking the gain region of the semiconductor optical amplifier to be a nonlinear optical medium as disclosed in Japanese Patent Application Laid-open No. 2000-66253, has the following problem. That is, a lens must be used in order to optically connect the semiconductor optical amplifier to an optical fiber which is the communication path of an optical communication system, and a process of precise position adjustment is necessary in order to determine the positional relationship of the lens, the semiconductor optical amplifier, and the optical fiber. Difficulty is involved in the process of position adjustment to cause light emitted from the semiconductor optical amplifier to be incident on the optical fiber with low loss, and due to various elements such as the propagation mode of light propagating through the optical waveguide of the semiconductor optical amplifier, the condensing characteristics of the lens, and the numerical aperture of the optical fiber, there are limits beyond which the connection loss cannot be reduced further.
Also, the wavelength of light obtained through wavelength conversion is determined uniquely by the wavelength of the signal light and the wavelength of the pump light, so that there is the constraint that conversion into light of an arbitrary wavelength is not possible. This is also a major technical constraint imposed on construction of a WDM optical communication system.
In the wavelength conversion device using a multiple-wavelength light source disclosed in Japanese Patent Application Laid-open No. 2001-251253, it is necessary to incorporate a new multiple-wavelength light source device into the wavelength conversion device, and consequently power consumption is increased. Reduction of this power consumption is a technical problem. Also, because numerous devices and components are necessary, such as a clock signal generator, signal regenerator and control circuit, there is the problem that the wavelength conversion itself becomes complicated, and productivity worsens.
Moreover, devices such as a clock signal generator, signal regenerator and control circuit generally only operate at limited frequencies. Hence the bit rate of an optical communication system thus constructed is limited, and, for example, it is difficult to achieve higher bit rates.
Hence an object of this invention is to provide a wavelength conversion device with a broad range of selection of light wavelengths obtained through conversion.